Aluminum porous body and fabrication method of same

ABSTRACT

It is an objective of the present invention to provide an aluminum porous body which is formed of a pure aluminum and/or aluminum alloy base material and has excellent sinterability and high dimensional accuracy without employing metal stamping. There is provided an aluminum porous body having a relative density of from 5 to 80% with respect to the theoretical density of pure aluminum, in which the aluminum porous body contains 50 mass % or more of aluminum (Al) and from 0.001 to 5 mass % of at least one selected from chlorine (Cl), sodium (Na), potassium (K), fluorine (F), and barium (Ba). It is preferred that the aluminum porous body further contains from 0.1 to 20 mass % of at least one selected from carbon (C), silicon carbide (SiC), iron (II) oxide (FeO), iron (III) oxide (Fe 2 O 3 ), and iron (II,III) oxide (Fe 3 O 4 ).

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationserial no. 2010-084772 filed on Apr. 1, 2010, the content of which ishereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an aluminum porous body and a method offabricating the same.

2. Description of Related Art

Aluminum porous bodies are used as heat-exchanger materials, filtermaterials, shock/vibration-absorbing materials,sound-insulating/absorbing materials, and the like. An aluminum porousbody is fabricated usually by molding a base material (e.g., powdermaterial, chip material, fibrous material) of pure aluminum or aluminumalloy into a desired shape and joining the contact points of the basematerial by sintering or brazing.

Meanwhile, a base material of pure aluminum or aluminum alloy is knownas a sintering-resistant material since it generally forms a coating ofalumina (Al₂O₃), which is thermally very stable, on a surface thereof.Therefore, in order to obtain a sintered body of a pure aluminum basematerial or an aluminum alloy base material, it is necessary to subjectthe base material to high deformation at a molding stage to break theAl₂O₃ coating on the surface and to promote contact between newly-formedsurfaces before subjecting the base material to liquid-phase sinteringin the solid-liquid coexistence region.

For example, JP-A 2004-285410 discloses an aluminum porous body having abulk density of not less than 0.20 g/cm³ and not more than 1.20 g/cm³.This aluminum porous body is obtained by cutting an aluminum cladmaterial formed of an aluminum or aluminum alloy material clad with abrazing filler metal of aluminum alloy to form chips containing thebrazing material, by molding the chips into a predetermined shape, andby subjecting the molded piece to brazing. The contact point joiningpercentage between the chips is not less than 25% and less than 50%.

Unfortunately, with conventional techniques such as the one describedabove, it is difficult to fabricate a porous body having a complex shapesince conventional techniques inevitably involve molding a base materialinto a desired shape by metal stamping or the like as a preliminary stepprior to the sintering or brazing process. Moreover, conventionaltechniques tend to be costly since each change in shape requires a newstamping die.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an objective of the present invention tosolve the above-described problems and to provide an aluminum porousbody which is formed of a pure aluminum and/or aluminum alloy basematerial and has excellent sinterability and high dimensional accuracywithout employing metal stamping. Furthermore, it is another objectiveof the invention to provide a method of fabricating such an aluminumporous body.

(I) According to one aspect of the present invention, there is providedan aluminum porous body having a relative density of from 5 to 80% withrespect to the theoretical density of pure aluminum, in which thealuminum porous body contains 50 mass % or more of aluminum (Al) andfrom 0.001 to 5 mass % of at least one selected from chlorine (Cl),sodium (Na), potassium (K), fluorine (F), and barium (Ba).

In the above aspect (I) of the present invention, the followingimprovements and modifications can be made.

(i) The aluminum porous body further contains from 0.1 to 20 mass % ofat least one selected from carbon (C), silicon carbide (SiC), iron (II)oxide (FeO), iron (III) oxide (Fe₂O₃), and iron (II,III) oxide (Fe₃O₄).

(II) According to another aspect of the present invention, there isprovided a method of fabricating an aluminum porous body, in which themethod comprises the steps of: mixing a raw material powder of purealuminum and/or aluminum alloy with an aluminum brazing flux; shapingthe raw material powder via the flux by irradiating the raw materialpowder mixed with the flux with a laser; and sintering the raw materialpowder by irradiating the shaped raw material powder withelectromagnetic waves.

In the above aspect (II) of the present invention, the followingimprovements and modifications can be made.

(ii) The frequency of the electromagnetic waves ranges from 900 MHz to30 GHz.

(iii) The aluminum brazing flux is a chloride-based flux orfluoride-based flux.

(iv) The chloride-based flux is mainly composed of barium chloride(BaCl₂), sodium chloride (NaCl), potassium chloride (KCl), or zincchloride (ZnCl₂).

(v) The fluoride-based flux is mainly composed of aluminum fluoride(AlF₃), potassium tetrafluoroaluminate (KAlF₄), potassiumpentafluoroaluminate (K₂AlF₅), or potassium hexafluoroaluminate(K₃AlF₆).

Advantages of the Invention

According to the present invention, it is possible to provide analuminum porous body that is formed of a pure aluminum and/or aluminumalloy base material and has excellent sinterability and high dimensionalaccuracy without employing metal stamping. Also, it is possible toprovide a method of fabricating such an aluminum porous body. As aresult, a porous body having a complex shape can be easily provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of microwave heating of an aluminum porousbody in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In recent years, product development cycles have become shorter andthere is a growing need for producing prototypes rapidly and easily(i.e. at low cost). One solution to meet the need is rapid prototyping(hereinafter referred to as RP), which is a 3D modeling method to createonly the outside shape of an object rapidly. RP is widely used toproduce machine parts having complex shapes, prototypes based on whichthe suitability of industrial products of high esthetic quality ischecked, or the like.

A technique for RP is called additive manufacturing, with which amultiplicity of thin unit layers are stacked to form a shape. Morespecifically, layers of a powder material are laid down and irradiatedwith a laser so that the powder is directly sintered or its particlesare joined via a binder. In the case of a metallic powder, the surfacesof its particles are coated with a binder, or the metallic powder ismixed with a binder powder, and the binder is melted by laserirradiation so that the powder particles are joined to form a shape(preform), and then the metallic powder is sintered. In this way, withRP, complex-shaped structures which are difficult to make by metalstamping can be produced rapidly.

The most important feature (advantage) of the present invention residesin the fact that an aluminum porous body that has excellentsinterability and high dimensional accuracy can be provided withoutemploying metal stamping, even though it is formed of a pure aluminum-and/or aluminum alloy-based powder, which is a sintering-resistantmaterial, and even if it has a complex shape. Therefore, the aluminumporous body and the method of fabricating the same in accordance withthe present invention can be preferably applied to RP.

Here, there is no particular limitation on the particle shape of thepure aluminum- and/or aluminum alloy-based powder used in an embodimentof the present invention as long as the size specifications describedbelow are met. Also, aluminum alloy is defined as alloy containing atleast 50 mass % of aluminum.

An embodiment of the present invention will be described hereinafterwith reference to the accompanying drawing. In this regard, however, thepresent invention is not limited to the embodiment disclosed herein, andcombinations and improvements may be made as appropriate withoutdeparting from the spirit and scope of the present invention.

As described before, a coating of Al₂O₃, which is thermally very stable,is formed on the surface of each particle of pure aluminum or aluminumalloy powder (hereinafter referred to as Al-system metallic powder),inhibiting the sintering of the powder particles. The inventors devotedthemselves to study the sintering behavior of Al-system metallic powderand thought that if a liquid phase was created in the surface region ofAl-system metallic powder particles by selectively heating the surfacesof Al-system powder particles, the Al₂O₃ coating would be pushed away toexpose newly-formed surfaces (virgin surfaces) by the surface tensioneffect of the liquid phase, thus making it possible to sinter theparticles.

Here, it is difficult to produce a liquid phase only in the surfaceregion of each particle by typical electric-heater heating (radiationheating from outside). In the present invention, in contrast, thesurface region of each particle is heated intensively by irradiation ofelectromagnetic waves at frequencies of 900 MHz to 30 GHz, making itpossible to create a liquid phase in the surface region of eachparticle. However, in the case of heating metallic powder byelectromagnetic irradiation, it is important to effectively insulate themetallic powder from the atmosphere since plasma otherwise would begenerated and severe chemical reactions with the atmosphere would occur.

In the present invention, Al-system metallic powder is effectivelyinsulated from the atmosphere by mixing an aluminum brazing flux in theAl-system metallic powder, thus making it possible to sinter theAl-system metallic powder by electromagnetic irradiation. In addition,since the aluminum brazing flux softens by laser irradiation, it alsoserves as an adhesive that bonds Al-system metallic powder particles,making it possible to produce a preform without employing metalstamping. In other words, the aluminum brazing flux also serves as abinder in additive manufacturing of RP, making it possible to fabricatea complex-shaped structure.

Although Al-system metallic powder can be induction-heated byelectromagnetic irradiation, when the powder particle is small and theparticle size becomes 1 mm or smaller, heating at frequencies of severalkHz or so is difficult. In order to heat Al-system metallic powder witha particle size of 1 mm or smaller, the frequency range must be from 300MHz to 300 GHz or so (the frequency range for the so-called microwaves).Meanwhile, the particle size is preferably 500 μm or smaller forimproved sinterability of Al-system metallic powder. Also, in terms ofworkability, the particle size is preferably 0.5 μm or larger. As aresult, in order to effectively heat Al-system metallic powder with aparticle size of from 0.5 to 500 μm, it is preferred to use microwavesat frequencies ranging from 900 MHz to 30 GHz.

In general, when metal is heated by irradiating electromagnetic waves(microwaves), the electric current is concentrated on the surface of atarget object by a skin effect. The degree of current concentration isreferred to as current penetration depth. The current penetration depthdepends on the frequency, and it becomes shallower as the frequencybecomes higher. Therefore, by irradiating metallic powder withelectromagnetic waves (microwaves), the surface region of each powderparticle can be heated intensively.

In this regard, however, under microwave irradiation, chemical reactionsbetween metallic powder and the atmosphere tend to become severe. Forexample, in the case of microwave-heating pure aluminum powder innitrogen (N₂), Al combines with N₂ to generate aluminum nitride (AlN),making it difficult to sinter the aluminum powder particles. Meanwhile,inert gases such as argon (Ar) and helium (He) do not react with metal.However, they are easily brought into the state of plasma undermicrowave irradiation, often resulting in localized melting of metallicpowder or hot spots. Therefore, they are ill suited as atmosphericgases. In addition, although plasma generation and chemical reactionsbetween metallic powder and the atmosphere can be controlled under ahigh vacuum atmosphere of 1×10⁻² Pa or less, a costly vacuum pumpingsystem is required and a lot of time is also required for vacuumpumping.

In the present invention, as described above, chemical reactions betweenAl-system metallic powder and the atmosphere, which tend to occur undermicrowave irradiation, can be prevented by effectively insulating theAl-system metallic powder from the atmosphere by mixing an aluminumbrazing flux in the Al-system metallic powder. Preferable aluminumbrazing fluxes include chloride-based fluxes (e.g., fluxes mainlycomposed of BaCl₂, NaCl, KCl, or ZnCl₂) and fluoride-based fluxes (e.g.,fluxes mainly composed of AlF₃, KAlF₄, K₂AlF₅, or K₃AlF₆). Mixing thesefluxes in Al-system metallic powder allows sintering by microwaveirradiation even in the air atmosphere or N₂.

The surface of each particle of Al-system metallic powder can bemoistened by setting the content of the flux mixed with the Al-systemmetallic powder at from 0.01 to 20 mass % (not less than 0.01 mass % andnot more than 20 mass %), more preferably 0.01 to 10 mass %, and as aresult the above-described effect is produced. If the content is morethan 20 mass %, excessive contraction occurs during sintering, whichadversely affects the dimensional accuracy of the finished product.

Although it is preferred that the flux be removed by washing after thesintering process, it may not be fully removed and part of it mayremain. If the content of the remaining flux is 5 mass % or less, themechanical strength of the sintered porous body remains almostunaffected. When a chloride-based flux is used, the less content ofresidual chloride, the better. If the residual chloride content in thesintered porous body is around 0.01 mass %, more preferably around 0.001mass %, effects on the base material (e.g. corrosion) can be virtuallyignored. For these reasons, the sintered aluminum porous body containsfrom 0.001 to 5 mass % of at least one flux component selected from Na,Cl, K, F, and Ba.

In the case of sintering Al-system metallic powder by microwaveirradiation, when the relative density of the porous body exceeds 80%with respect to the theoretical density of pure aluminum, microwaves areprevented from penetrating the porous body, which makes intensiveheating in the surface region of each particle by a skin effectdifficult. Therefore, the upper limit on the relative density of theporous body is set at 80%.

Meanwhile, effective methods for reducing the relative density of theporous body (i.e., increasing its porosity) include a spacer method. Inthe case of Al-system metallic powder, NaCl can be preferably used as aspacer material. The relative density of an aluminum porous bodyfabricated by means of a spacer method can be reduced down to around 5%(maximum porosity: around 95%). In other words, according to the presentinvention, the relative density of an aluminum porous body can becontrolled from 5 to 80%.

In the case of heating metallic powder by microwave irradiation, theheating behavior is strongly affected by the output of microwaves, themethod of irradiation, etc. Particularly when the so-called multimodeoven is used as a microwave applicator, the heat produced in specimensto be heat-treated is small and may not reach the sintering temperature.In such a case, heat production can be promoted by mixing a powderedmicrowave absorber (e.g., C, SiC, FeO, Fe₂O₃, and Fe₃O₄) in Al-systemmetallic powder. In this regard, however, adding too much of themicrowave absorber rapidly increases the temperature and makestemperature control difficult. Therefore, it is preferred that theabsorber content be 20 mass % or less.

On the other hand, when a single-mode oven is used as the microwaveapplicator, the specimens can be heated up to the sintering temperaturewithout adding any powdered microwave absorber such as C, SiC, FeO,Fe₂O₃, and Fe₃O₄. However, adding around 0.1 mass % or more of apowdered microwave absorber increases the heating efficiency, and theAl-system metallic powder can be heated to the sintering temperaturewith less energy. Therefore, an aluminum porous body in accordance withthe present invention preferably contains from 0.1 to 20 mass % of amicrowave absorber such as C, SiC, FeO, Fe₂O₃, and Fe₃O₄.

FIG. 1 is a schematic view of microwave heating of an aluminum porousbody in accordance with an embodiment of the present invention. The fluxirradiated with a laser in RP partly melts and bonds the Al-systemmetallic powder particles. Then, as shown in FIG. 1, while being heatedto the sintering temperature by microwave irradiation, the flux meltsand moistens the surfaces of the Al-system metallic powder particles,thereby effectively insulating the Al-system metallic powder particlesfrom the atmosphere and preventing chemical reactions between them. As aresult, the Al-system metallic powder particles can be sinteredeffectively.

As described above, according to the present invention, the mixture ofAl-system metallic powder, an aluminum brazing flux powder, a powderedmicrowave absorber, and a spacer material as needed is irradiated with alaser so that the flux is melted and these powders can be provisionallyshaped without pressure. In other words, they can be shaped by RP. Thisprocess is followed by a sintering process by the irradiation ofelectromagnetic waves (microwaves), thereby making it possible tofabricate an aluminum porous body having high dimensional accuracyand/or a complex structure in a short period of time.

Moreover, the aluminum porous body in accordance with the presentinvention can be used as an ultra-lightweight material,high-specific-rigidity material, energy-absorbing material,vibration-absorbing material, electromagnetic wave-absorbing material,sound-insulating material, sound-absorbing material, heat-insulatingmaterial, electrode material, filter material, heat-exchanger material,biomedical material, oil-impregnated bearing material, etc.

EXAMPLES

An embodiment of the present invention will be described hereinafter onthe basis of an example. However, the present invention is not to beconsidered limited to this.

In the example, the inventors used pure Al powder and AC4B (Al—Si—Cucasting alloy) powder (each 150 μm or smaller in particle size) asAl-system metallic powder, AlF₃ (50 μm or smaller in particle size) as afluoride-based flux, NaCl (500 μm or smaller in particle size) as aspacer material, and SiC (5 μm or smaller in particle size) as amicrowave absorber. A powdered pure Al base material and a powdered AC4Bbase material were prepared by mixing these powders using a V-mixer suchthat each mixture contains 25 mass % of Al-system metallic powder, 3mass % of the flux, 2 mass % of the microwave absorber, and 70 mass % ofthe spacer material.

Each powder mix was provisionally formed into a circular cylindricalshape having 10 mm of diameter and 10 mm of height (φ10×10) by RP. RPwas performed under conditions that the laser power was 15 W (beamdiameter: 0.4 mm), the laser scanning speed was 7.6 m/sec., and thestack pitch was 0.1 mm.

Next, each sample of φ10×10 provisionally formed by RP was irradiatedwith microwaves at a frequency of 2.45 GHz in a single-mode microwaveoven. The sintering process was carried out in a nitrogen atmospherewhile applying a magnetic field. The microwave output was controlledsuch that the sintering temperature for the powdered pure Al basematerial was 645° C. and the sintering temperature for the powdered AC4Bbase material was 570° C. The times to reach the sintering temperatureswere measured. The holding times at the sintering temperatures werechanged in the range of 5 to 30 minutes. For comparison, specimens werealso fabricated by sintering preforms shaped in a similar way byelectric-heater heating using a typical heating oven under the sameconditions of sintering temperature and time. Each of the specimens wassubjected to ultrasonic cleaning in water to remove the spacer materialafter the sintering process.

Relative density measurement and appearance inspection were conducted oneach sample. The relative density of each sample was calculated withrespect to the theoretical density of pure aluminum (2.7 g/cm³) from thebulk density of the specimen measured on the basis of its size andweight. The added spacer material (NaCl) was assumed to have been elutedentirely by the ultrasonic cleaning. Also, the appearance of eachspecimen was evaluated visually. Table 1 shows the results of theexperiment in which specimens provisionally shaped by RP were sinteredby microwave heating and electric-heater heating.

TABLE 1 Experimental Results Time to Reach Sintering Holding RelativeTemperature Time Density Appear- Preform (min) (min) (%) ance MicrowavePowdered Pure 8 5 21 G Heating Al Base Material 10 22 G 30 23 R PowderedAC4B 5 5 24 G Base Material 10 24 G 30 23 R Electric- Powdered Pure 35 5— D heater Al Base Material 10 — D Heating 30 — D Powdered AC4B 27 5 17R Base Material 10 19 R 30 24 R Evaluation of Appearance G: Good, R:Roughness or Shape Change, and D: Degradation.

In the case of microwave heating, the time required for heating wasshort, and both of the powdered pure Al base material and the powderedAC4B base material could be heated to the target sintering temperaturein 5 to 8 minutes. As a result of sintering the powder particles, porousbodies were fabricated. With either of the base materials, minorroughness (asperities) was observed partially on the surfaces of thespecimens sintered for 30 minutes. However, there was little variationin relative density for different sintering times, and even with a shortsintering time of 5 minutes, a nearly ideal relative density wasobtained corresponding to the amount of the added NaCl spacer material.

In contrast, in the case of electric-heater heating, the time requiredto reach the target sintering temperature varied from 27 to 35 minutes,roughly 5 times the time of microwave heating. With the powdered pure Albase material, sintering was partly insufficient for either sinteringtime. Because the specimens degraded at the time of ultrasonic cleaning,relative densities could not be evaluated. With the powdered AC4B basematerial, significant roughness was observed for all the sinteringtimes, and the shape itself changed when the sintering time is long. Inthe case of electric-heater heating, because temperature rising andcooling slow down due to the heat capacity of each specimen as a whole,the residence time at temperatures around the sintering temperaturebecomes long, and the surface of each specimen is heated most due toradiation heating, which was considered to have adversely affected theappearance and dimensional accuracy of the specimen.

These experimental results have demonstrated that an aluminum porousbody having a high dimensional accuracy can be fabricated by heattreatment in a shorter time than ever.

Although the invention has been described with respect to the specificembodiments for complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A method of fabricating an aluminum porous body,comprising the steps of: mixing an aluminum brazing flux with a rawmaterial powder, the brazing flux comprising at least one of achloride-based flux including zinc chloride and a fluoride-based fluxincluding aluminum fluoride, and the raw material powder comprising atleast one of pure aluminum and aluminum alloy; controlling the relativedensity of the aluminum porous body within a range of from 5 to 80% withrespect to the theoretical density of pure aluminum by mixing a spacermaterial with the aluminum brazing flux and raw material powder; andshaping the raw material powder via the flux by irradiating the rawmaterial powder mixed with the flux with a laser; and sintering the rawmaterial powder by irradiating the shaped raw material powder withelectromagnetic waves; and removing the flux and the spacer material bywashing after sintering.
 2. The method of fabricating an aluminum porousbody according to claim 1, wherein the frequency of the electromagneticwaves ranges from 900 MHz to 30 GHz.
 3. The method of fabricating analuminum porous body according to claim 2, wherein the particle size ofthe raw material powder is from 0.5 to 500 μm.
 4. The method offabricating an aluminum porous body according to claim 1, wherein themixture of the aluminum flux and raw material powder has a flux contentfrom 0.01 to 20 mass percent.
 5. The method of fabricating an aluminumporous body according to claim 1, wherein the spacer material comprisessodium chloride.
 6. The method of fabricating an aluminum porous bodyaccording to claim 1, wherein the spacer material comprises a materialhaving heat resistance to withstand a sintering temperature in thesintering step and being soluble in water in the removing step.
 7. Themethod of fabricating an aluminum porous body according to claim 1,further comprising the step of: increasing the heating efficiency by theelectromagnetic waves by mixing 0.1 to 20 mass percent of a powderedmicrowave absorber with the aluminum flux and raw material powder.
 8. Amethod of fabricating an aluminum porous body comprising the steps of:mixing an aluminum brazing flux with a raw material powder, the brazingflux comprising at least one of a chloride-based flux including zincchloride and a fluoride-based flux including aluminum fluoride, and theraw material powder comprising at least one of pure aluminum andaluminum alloy; shaping the raw material powder via the flux byirradiating the raw material powder mixed with the flux with a laser;increasing the heating efficiency by electromagnetic waves by mixing 0.1to 20 mass Percent of a powdered microwave absorber with the aluminumflux and raw material powder; and sintering the raw material powder byirradiating the shaped raw material powder with electromagnetic waves,wherein the powdered microwave absorber is selected from groupconsisting of carbon, silicon carbide, iron (II) oxide, iron (III) oxideand iron (II, III) oxide.
 9. A method of fabricating an aluminum porousbody, comprising the steps of: mixing an aluminum brazing flux with araw material powder, the brazing flux comprising at least one of achloride-based flux and a fluoride-based flux, and the raw materialpowder comprising at least one of pure aluminum and aluminum alloy;mixing a spacer material with the aluminum flux and raw material powder;shaping the raw material powder via the flux by irradiating the rawmaterial powder mixed with the flux with a laser; and sintering the rawmaterial powder by irradiating the shaped raw material powder withelectromagnetic waves; and removing the flux and the spacer material bywashing after sintering.
 10. The method of fabricating an aluminumporous body according to claim 9, wherein the aluminum brazing fluxcomprises a chloride-based flux including at least one of bariumchloride, sodium chloride, potassium chloride, and zinc chloride. 11.The method of fabricating an aluminum porous body according to claim 9,wherein the aluminum brazing flux comprises a fluoride-based fluxincluding at least one of aluminum fluoride, potassiumtetrafluoroaluminate, potassium pentafluoroaluminate, and potassiumhexafluoroaluminate.
 12. The method of fabricating an aluminum porousbody according to claim 9, wherein the mixture of the aluminum flux andraw material powder has a flux content from 0.01 to 20 mass percent. 13.The method of fabricating an aluminum porous body according to claim 9,wherein the spacer material comprises sodium chloride.
 14. The method offabricating an aluminum porous body according to claim 9, furthercomprising the step of: mixing 0.1 to 20 mass percent of a powderedmicrowave absorber with the aluminum flux and raw material powder. 15.The method of fabricating an aluminum porous body according to claim 9,wherein the frequency of the electromagnetic waves ranges from 900 MHzto 30 GHz.
 16. A method of fabricating an aluminum porous bodycomprising the steps of: mixing an aluminum brazing flux with a rawmaterial powder, the brazing flux comprising at least one of achloride-based flux and a fluoride-based flux, and the raw materialpowder comprising at least one of pure aluminum and aluminum alloy;shaping the raw material powder via the flux by irradiating the rawmaterial powder mixed with the flux with a laser; mixing 0.1 to 20 masspercent of a powdered microwave absorber with the aluminum flux and rawmaterial powder; and sintering the raw material powder by irradiatingthe shaped raw material powder with electromagnetic waves, wherein thepowdered microwave absorber is selected from group consisting of carbon,silicon carbide, iron (II) oxide, iron (III) oxide and iron (II, III)oxide.